Anti-Listeria activity of Lactococcus lactis subsp. lactis LAB3 cells entrapped in alginate beads: effects of inoculum size, alginate beads formulation and atmosphere composition

Yan HEPascal DEGRAEVENadia OULAHAL^*

• Université Claude Bernard Lyon 1, Lyon, France

Bioprotective Lactococcus lactis LAB3 cells producing bacteriocin-like substances were entrapped in 4% (w/w) sodium alginate matrices supplemented or not with 10% (w/w) sodium caseinate. The effects of beads formulation (alginate alone or combined with caseinate, addition or not of either 20% (w/w) MRS broth, or M17 broth) on the evolution of the culturability of Lc. Lactis LAB3 cells entrapped in beads and on their anti-Listeria activity over 12 days storage at 30°C in closed bottles were investigated.Calcium-alginate-caseinate beads with MRS broth were the best system to preserve both culturability and anti-Listeria activity of Lc. lactis LAB3 cells. Inoculum size (~10 6 or ~10 8 CFU mL -1 initially) also played a role: only the higher initial inoculum load resulted in a significant anti-Listeria activity of beads after 12 days at 30°C, despite a decreasing anti-Listeria activity over time, likely due to rapid nutrient depletion. In order to evaluate the possibility to combine modified atmosphere packaging with Lc. lactis LAB3 bioprotective strain addition for perishable foods preservation, a prerequisite was to evaluate whether anti-Listeria activity was maintained after 4 days storage at 30°C of calcium-alginate caseinate beads with either MRS or M17 broth in 3 different atmospheres. While beads entrapping Lc. lactis LAB3 cells stored in a 20% (v/v) O2 -80% (v/v) N2 and in a 60% (v/v) O2 -40% (v/v) N2 atmosphere kept their anti-Listeria activity, anti-Listeria activity of beads entrapping Lc. lactis LAB3 cells stored in a 20% (v/v) CO2 -80% (v/v) N2 atmosphere was impaired.